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The ESO’s ELT M4 adaptive mirror is based on the large, contactless voice-coil adaptive mirror technology, with 5352 actuators controlling the shape of the six mirror segments. The system will dissipate up to 8 kW, which are removed by a direct gas expansion cooling system, specifically designed for the application. The key advantage of such solution is related to the fact that any possible leakage from the cooling system would not cause damages to the optics and electronics of the M4 only, but also potentially to the ones of M1, M3 and M5; with AdOptica’s system, the gas spillage would cause a local evaporation with consequent temperature drop, without any further consequences.
The whole cooling system, including the evaporator embedded in the M4 and the dedicated compressor unit, have been completely assembled. To facilitate the testing and calibration, we designed and built a dedicated large evaporator test unit, called Heat Load Emulator: such device allowed testing and tuning the whole cooling system over the full functional power and environmental ranges, well before the integrated M4 became available, without putting at risk the precious M4 embedded control system.
In this work we present the overall cooling system, the dedicated test setup and performance tests results.
The unit has entered the final design and construction phase in July 2015, after an advanced preliminary design. The final design review is planned for fall 2017; thereafter, the unit will enter the construction and test phase. Acceptance in Europe after full optical calibration is planned for 2022, while the delivery to Cerro Armazones will occur in 2023.
Even if the fundamental concept has remained unchanged with respect to the other contactless large deformable mirrors, the specific requirements of the E-ELT unit posed new design challenges that required very peculiar solutions. Therefore, a significant part of the design phase has been focused on the validation of the new aspects, based on analysis, numerical simulations and experimental tests. Several experimental tests have been executed on the Demonstration Prototype, which is the 222 actuators prototype developed in the frame of the advanced preliminary design. We present the main project phases, the current design status and the most relevant results achieved by the validation tests.
In this paper we present some of the major results obtained and challenges encountered during the phase of System Tests, like the preparation of the Acquisition sequence, the testing of the Jitter loop, the performance optimization in GLAO and the offload of low-order modes from the DSM to the telescope (restricted to the M2 hexapod). The System Tests concluded with the successful acceptance, shipping, installation and first commissioning of GRAAL in 2015 as well as the acceptance and shipping of GALACSI, ready for installation and commissioning early 2017.
The deformable secondary mirror of VLT: final electro-mechanical and optical acceptance test results
Layer-oriented multiconjugate adaptive optics systems: performance analysis by numerical simulations
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